Centralized radio system for short and broadcast waves



Examiner ted Orl back 0f this Sheet.

Sept. 6, 1938.

J. WEINBEBGER CENTRALIZED RADIO SYSTEM FOR SHORT AND BROADCAST WAVESFiled Feb. 19, 1936 .t mx

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INVENTOR. J. WEINBERGER 7 .J ,Z ATTORNEY.

Patented Sept. 6, 1938 UNITED STATES Examiner PATENT OFFICE CENTRALIZEDRADIO SYSTEM FOR SHORT AND BROADCAST WAVES Julius Weinberger,Bronxville, N. Y., assigner to Radio Corporation of America, acorporation of Delaware Application February 19, 1936, Serial No. 64,657

6 Claims.

'I'he object of this invention is to obtain a reception and distributionsystem for centralized radio installations of the radio frequencydistribution type, which will be capable of distributing not only thenormal broadcast band of frequencies (e. g. 550 to 1,500 k. c.) but alsothe so-called short-wave band (e. g. 5 to 20 megacycles) on whichinternational broadcasting is carried on.

The trend in modern radio receivers is towards the all-wave type,capable of receiving both normal broadcast and the above-mentioned shortwaves. When such a. receiver is used in connection with present types ofcentralized radio systems, it is ineffective for short wave reception,because these systems are only designed to distribute the normalbroadcast waves.

In my invention, a system is shown which is capable of receiving anddistributing both bands of waves. The attached figure illustrates oneembodiment of the invention.

Referring to this figure, I is an antenna which is designed to receivenormal broadcast waves, and which ls connected through resistance 2 toground. Across 2 are connected the input terminals of vacuum tube 3. Theplate circuit of this tube is connected to the primary of the radiofrequency step-down transformer 4 which is designed to couple the tubeelciently to the radio frequency transmission line 5 over the normalbroadcast band of frequencies. Resistor 2 is chosen of a suillcientlyhigh value such that the amplier 3 is aperiodic and thus amplfiescurrents of the different frequencies of the broadcast bandsubstantially equally. A low pass filter comprising condensers Ii, 6 andinductance coils 1, I designed to have a cut off at a frequency somewhatabove the broadcast band but below the short wave band, for example, at3,000 kilocycles, is introduced between transformer 4 and line 5. 'I'hisfilter transmits currents of the broadcast band eiciently and at thesame time prevents the short wave signals from being affected by thelosses which would be introduced were they passed through the secondaryof transformer 4. For efficient transmission the transformer I may bedesigned to match the impedance of the low pass filter to the plateimpedance of the tube for the broadcast band of frequencies. Condenser6' is chosen to have a very low impedance, or act as a by-pass, forcurrents of the short wave band.

As shown, a short wave antenna 8 which may be of any type efficient atshort waves, such as a doublet antenna, has its opposite halvesconnected to the ends of a. resistor I by a trans- (Cl. Z50-9) missionline 9, the center of resistor Il preferably being grounded as shown.The ends of the resistor are connected to the grids of a pair ofpush-pull tubes II, II', which serve as an aperiodic amplifier forcurrents of the short wave band. 'I'he plate circuits of these tubes areshown as connected to the line by a transformer I2 whose secondarywinding 20 is connected in series with line 5. For the short wavesignals the antenna system 8 causes the control grids of tubes II, II tobe in substantially opposite phase so that they operate as a push-pullamplifier to cause amplification of the incoming signal currents,whereas any signal currents of the broadcast band picked up by antenna 8cause the two grids to be operated substantially in phase, so that theeffects are balanced out in their plate circuits due to the connectionof the plate voltage supply at the midpoint of primary winding I5.Transformer I2 is preferably designed to match the plate impedance oftubes II, Il to that of transmission line 5 and would ordinarily be astep-down transformer.

Transmission line 5 is a specially designed cable 4 of such low capacitythat it will transmit currents of both the broadcast and short wavebands to a. plurality of radio receivers Il located at spaced pointsalong the line, such as in the different rooms of a building or vessel.This line may comprise a. hollow metal pipe 5', of brass or copper, andwhich may be grounded as shown, and connected by a lead I 6 to one sideof the' low pass filter. The high potential side of the line 5 comprisesa fine copper wire 25 connected to one end of secondary coil 20 by alead II. Wire 26 is mounted within pipe 5 and is supported therein atits center by a plurality of spaced insulating washers I 8. The line maybe terminated at its far end by a, resistor I3 in such manner as toavoid reflection currents from the end of the line, as by making thevalue of the resistor equal to the surge impedance of the line. Asshown, the ground terminals G of the radio receivers I4 are connected topipe 5 and their high potential or antenna terminals A to the wire 26,the pipe serving as a very convenient ground connection for the severalreceivers. The pipe 5' also serves as a shielding sheath to prevent theline from picking up noise currents or undesired signal currents.

It will be understood that one or more of the radio receivers I4includes a suitable selecting or tuning means whereby any desiredstation transmitting within either the broadcasting or short wave bandsmay be received. Such selecting means, being well known to those skilledin the art, is omitted for simplicity of illustration.

While I have described a single embodiment of my invention, it will beunderstood that the invention is not limited thereto, but embraces allsuch structures and combinations as come within the scope of theappended claims.

What I claim is:

1. In a wave transmission system, the combination of a long transmissionline adapted to pass currents of the broadcast band and the short waveband, an antenna adapted to pick up cur-l rents of the broadcast band,an aperiodic amplier having its input circuit connected to said antennaand its output circuit coupled to one end of said transmission line, anantenna arranged to pick up currents of the short wave band, a secondaperiodic amplifier having its input circuit connected to said lastnamed antenna and its output circuit coupled to the same end of saidtransmission line and a condenser shunted across the first amplifieroutput circuit which has a low impedance to currents of the short waveband.

2. In a wave transmission system, the combination of a long transmissionline adapted to pass currents of the broadcast band and the short waveband, a grounded metallic shield for said transmission line, an antennaadapted to pick up signal currents of the broadcast band, an aperiodicamplier having an input circuit andan output circuit, said input circuitbeing connected to said antenna, a coupling means connected to saidoutput circuit, a low pass ilter having its input -terminals connectedto said coupling means and its output terminals to said transmissionline, a transformer having primary and secondary windings, saidsecondary winding being connected in series between said low pass iilterand one side of said transmission line, an antenna arranged to pick upcurrents of the short Wave band, an amplier having input and outputcircuits, means coupling said input circuit to said last named antennaand said output circuit including said transformer primary Winding, andat least one radio receiver having its input terminals connectedrespectively to said transmis-A sion line and said grounded shield.

3. The combination defined in claim 2in which said low pass ltercomprises a condenser connected across its output terminals, saidcondenser having a low impedance to currents of the short Wave band.

4. In a wave transmission system, the combination of a long transmissionline adapted to pass currents of the broadcast band and the short waveband, means for maintaining one side of said line at ground potential,an antenna adapted to pick up currents of the broadcast band, anaperiodic amplier having an input circuit connected to said antenna andits output circuit coupled to one end of said transmission line, a pairof vacuum tubes having control gridcathode circuits and plate circuits,an antenna` system arranged to pick up currents of the short wave band,means connecting said antenna system to said control grid-cathodecircuits to cause said control grids to operate substantially 180degrees out of phase, means coupling the plate circuits of said pair oftubes to said end of said transmission line, a condenser having a lowimpedance to currents of the short wave band connected between said lastnamed coupling means and the grounded side of said transmission line anda plurality of radio receivers connected across said tranen-selon line.

5. In a tran.; r t stem the combination of a hollow mei-V tube. a wirewithin said tube, a plurality of insulating washers arranged to supportsaid wire near the center of said tube, a plurality of radio receivershaving their ground terminals connected to said tube and their antennaterminals to said wire, a circuit connecting one end of said tube andwire and comprising the series connection of a long wave coupling deviceand a short wave coupling device, a long wave antenna, means couplingsaid antenna to said long wave coupling device, a short wave antenna,and means coupling said short wave antenna to said short wave couplingdevice.

6. In a device of the class described the combination of a transmissionline adapted to transmit currents of the short wave band and thebroadcast band, a source of signals of the broadcast band, a low passilter having a cut-oil frequency above the broadcast band but below theshort wave band connected to one end of said transmission line, meanscoupling said lter to said signal source, a source of signals of theshort wave band, means coupling said last named signal source to thesaid end of the transmission line, and means for maintaining one side ofsaid lter circuit at ground potential.

JULIU S WEIN'BERGER.

